Preheat oven to 350 degrees F.

In a medium-sized mixing bowl, mix together flour, salt, baking soda, and cream of tarter; set aside.

In the bowl of a standing mixer, cream butter and both granulated & powdered sugars together for 2 minutes until fluffy. Slowly stream in the oil while beating.

Add the vanilla and peppermint extract and then beat in the eggs one at a time until well combined.

Slowly add the flour mixture to the wet ingredients, mixing until combined (scrape down the sides of the bowl as needed). Mix in sprinkles.

Roll dough into 2 inch balls to make approx. 36 cookies. Place ¼ cup sugar in a small dish. Place rolled dough on a baking sheet about 3 inches apart. Using a drinking glass (or something that is 2.5 inches in diameter), dip into sugar. Press the glass into a ball of dough until it is ½ inch thick (the dough will form a jagged edge and spill past the edge of the glass).

Repeat the process of dipping the glass into sugar and pressing it into a ball of dough. Bake for 8 minutes only.

Gently remove cookies from pan onto a cooling rack and let them cool completely. Place them in an air tight Tupperware in the fridge.

Cream butter, sour cream and peppermint extract. Slowly add powdered sugar a little at a time. Add extra powdered sugar if needed to reach desired consistency.

Spread over cold cookies and serve immediately or let the icing dry (it will dry to the touch) and then store in an air-tight container in the fridge. Enjoy!